The present invention relates to a loudspeaker system for use in an automobile, and in more particular to a coaxial-type multi-speaker system for use in an automobile.
Improvement of the high-fidelity sound of loudspeaker systems has always been the object of much research. Coaxial-type multi-speaker systems have thus gained much wider acceptance of use in the automobile, and in spite of the advanced characteristics of such loudspeaker systems, results have been less than satisfactory when installed inside an automobile. In the past, various modifications have been proposed aimed at enhancing the realism of stereophonic reproduction in the environment of the automobile. These have included positioning of the tweeter and midrange transducer distinct of the low frequency transducer (U.S. Pat. No. 4,502,149), or the positioning of the tweeter and midrange transducer above the lower frequency transducer with central axes fixed at approximately 30 degree angle difference (U.S. Pat. No. 4,451,928). The present application is also concerned with the creation of improved stereophonic reproduction within the environment of the automobile, and in particular focuses on two problems common to the stereophonic reproduction of sound in the special environment of the automobile, and common to the above reference patents.
More specifically, one type distortion common to multi-speaker systems is crossfield phase distortion. Such distortion occurs at the frequency point where two transducers of differing sizes functioning together as a discrete channel meet, and is due to the time or phase difference between sound waves of the two transducers. Interference results, and the net effect is phase peaks, drops or cancellation, usually affecting midrange definition most severely. Attempts to rectify such include the placing of the higher frequency transducer at a point where the inner edge of the cone-shaped diaphram of both the higher and lower frequency transducers lie in the same plane, or the fixing of a time delay plate over the membrane of the higher frequency transducer.
The crossfield phase distortion of coaxial-type multi-speaker systems, such as are commonly used in automobiles, is obviously especially pronounced as sound waves of the higher frequency transducer will always be spatially in front of those of the lower frequency transducer. The small environment of the automobile is not suitable for application of the said time delay plate, and thus distortion results in the special environment of the automobile.
In addition, perception of stereophonic sound is basically contingent upon two conditions being met. The listener must be positioned so as to receive signals from the two discrete channels, and the signals thus received must be of the correct proportion as dictated by the originally recorded sound. In the special environment of the automobile, these two conditions can only be met at a point located center of the back seat. Passengers seated, as is usually the case, off-center of such point receive signals strongly from the channel fixed on their respective side and signals weakly from the channel fixed on the opposing side.
To solve the foregoing problems, the present application therefore proposes a coaxial-type multi-speaker system for use in a motor vehicle which includes a low frequency transducer, a high frequency transducer, and a specially designed cover of elongated substantially half-cylindrical periphery open at the two oppositely disposed lengthwise terminating ends, and inside the cover there are two sound reflector panels of V-shaped cross section mounted in double level fashion, one above the center of each transducer's membrane. The coaxial-type multi-speaker system thus constructed will separately divide the sound outputs of the high and low frequency transducers into two separate equal halves which will then be emitted from the two open ends of the cover in symmetrical fashion, and if the sound reflector panels are also fixed at distances relative to their respective transducers such as is capable of amending for the relatively faster moving sound waves of the higher frequency transducer, a total output relatively free of crossfield phase distortion may be obtained. Such a speaker system, if mounted on or under the rear parcel tray of a motor vehicle as the present application suggests, will utilize the rear window and side walls of said motor vehicle as sound reflecting barriers, and the passengers seated in the rear seats of such automobile will receive sound signals from the two discrete stereo channels relatively free of crossfield phase distortion and which most closely approximate the intended sound signal proportions as dictated by the originally recorded sound.
Also, prior art has frequently seen use of a cone-shaped reflector, usually utilized with a single low frequency transducer, mounted such that the apex point of the reflector is facing the center of the transducer's membrane. The purpose of this type reflector is production of an output of all directions, and this type transducer is commonly termed an omni-directional speaker. The present application is concerned with production of an output focused in two opposite directions and is not to be confused with such type speaker.